“My role will be to give every possible support to the next Conservative administration to make sure that we properly fulfil the mandate of the people that was delivered at the referendum and to champion the agenda I believe in.”

Mr Johnson had been the favourite to succeed David Cameron as Prime Minister until Mr Gove's sensational move.

Mr Gove, who was the most high-profile Conservative backing a Leave vote alongside Mr Johnson, declared his own candidacy this morning.

"I respect and admire all the candidates running for the leadership. In particular, I wanted to help build a team behind Boris Johnson so that a politician who argued for leaving the European Union could lead us to a better future.

"But I have come, reluctantly, to the conclusion that Boris cannot provide the leadership or build the team for the task ahead.”

Several senior Conservatives, including Nick Boles and Dominic Raab, also transferred their allegiance from Mr Johnson to Mr Gove.

Mr Johnson had made a speech highlighting his record as Mayor of London between 2008 and 2016.

And he set out the challenges facing the next Prime Minister:

“This is our chance to think globally again, to lift our eyes to the horizon and to bring our unique British voice and values, powerful humane progressive to the great global forums without being elbowed aside by a supranational body.

“And instead of being afflicted by it let us seize this chance and make this our moment to stand tall in the world. That is the agenda for the next prime minister of this country.”